How can i run app.js file

Hello. This app.js start to run when application is up. How can i start this file from code?

Code:

Ext.Loader.setConfig({ enabled: true });

Ext.application({
    name: 'ExtMVC',

    controllers: [
        'Portal'
    ],

    requires: [
        'Ext.layout.container.*',
        'Ext.resizer.Splitter',
        'Ext.fx.target.Element',
        'Ext.fx.target.Component',
        'Ext.window.Window',
        'ExtMVC.view.app.*',
        'ExtMVC.view.portal.*',
        'ExtMVC.view.portlet.*',
        'ExtMVC.view.Viewport',
    ],

    autoCreateViewport: true
    

});

How can i run app.js file